Effect of interfacial drag force on the numerical stability of the two-step method in the two-fluid model

1991 ◽  
Vol 126 (3) ◽  
pp. 427-438 ◽  
Author(s):  
Jae Young Lee ◽  
Hee Cheon No
Keyword(s):  
Drag Force ◽  
Numerical Stability ◽  
Fluid Model ◽  
Step Method ◽  
Two Fluid Model ◽  
Interfacial Drag ◽  
Two Fluid

Interfacial Drag Force Improvement in Two-Fluid Model

2018 ◽  
Author(s):  
Longxiang Zhu ◽  
Jianqiang Shan
Keyword(s):  
Drag Coefficient ◽  
Void Fraction ◽  
Drag Force ◽  
Fluid Model ◽  
Bubble Radius ◽  
Interfacial Area ◽  
Low Flow ◽  
Two Fluid Model ◽  
Interfacial Drag ◽  
Two Fluid

Interfacial drag force, which indicates the momentum transfer between liquid phase and vapor phase, is a key constitutive equation in the two-fluid model. Based on the “drift-velocity approach” (utilized in RELAP5/MOD3) and the “drag coefficient approach” (utilized in RELAP5/MOD2 and CTF), three improvements are proposed, which are: 1) improved drag coefficient closure, 2) improved drag coefficient formulation approach, 3) improved bubble radius closure approach. The comparison among the two original approaches and the three improved approaches has been made with the ORNL experiment data in high pressure-low flow condition and the results have been discussed. Results indicates: 1) the EPRI correlation predicts the void fraction worse than the drag coefficient approaches; 2) the drag coefficient correlations in CTF predicts the void fraction better than improved drag coefficient formulation approach, which are the original equations in Ishii’s model; 3) the improved drag coefficient formulation approach predicts similarly with the original RELAP5/MOD2 correlations, though it gets rid of the dependence on interfacial area concentration; 4) improved bubble radius closure approach over-predicts the void fraction, however more experiment tests should be calculated before a conclusion is drawn.

Interfacial drag force in one-dimensional two-fluid model

2012 ◽  
Vol 61 ◽  
pp. 57-68 ◽  
Author(s):  
Caleb S. Brooks ◽  
Takashi Hibiki ◽  
Mamoru Ishii
Keyword(s):  
Drag Force ◽  
Fluid Model ◽  
One Dimensional ◽  
Two Fluid Model ◽  
Interfacial Drag ◽  
Two Fluid

Effect of microstructural anisotropy on the fluid–particle drag force and the stability of the uniformly fluidized state

2012 ◽  
Vol 713 ◽  
pp. 27-49 ◽  
Author(s):  
William Holloway ◽  
Jin Sun ◽  
Sankaran Sundaresan
Keyword(s):  
Friction Coefficient ◽  
Drag Force ◽  
Fluid Model ◽  
Stokes Number ◽  
Spherical Particles ◽  
Force Model ◽  
Drag Model ◽  
Fluidized State ◽  
Two Fluid Model ◽  
Two Fluid

AbstractLattice-Boltzmann simulations of fluid flow through sheared assemblies of monodisperse spherical particles have been performed. The friction coefficient tensor extracted from these simulations is found to become progressively more anisotropic with increasing Péclet number, $Pe= \dot {\gamma } {d}^{2} / D$, where $\dot {\gamma } $ is the shear rate, $d$ is the particle diameter, and $D$ is the particle self-diffusivity. A model is presented for the anisotropic friction coefficient, and the model constants are related to changes in the particle microstructure. Linear stability analysis of the two-fluid model equations including the anisotropic drag force model developed in the present study reveals that the uniformly fluidized state of low Reynolds number suspensions is most unstable to mixed mode disturbances that take the form of vertically travelling waves having both vertical and transverse structures. As the Stokes number increases, the transverse-to-vertical wavenumber ratio decreases towards zero; i.e. the transverse structure becomes progressively less prominent. Fully nonlinear two-fluid model simulations of moderate to high Stokes number suspensions reveal that the anisotropic drag model leads to coarser gas–particle flow structures than the isotropic drag model.

Effect of Interfacial Pressure Term on Numerical Stability of a Two-Fluid Model

2014 ◽  
Author(s):  
Tomio Okawa ◽  
Yoshiro Kudo
Keyword(s):  
Numerical Stability ◽  
Two Phase Flow ◽  
Flow Boiling ◽  
Fluid Model ◽  
Phase Flow ◽  
Numerical Instability ◽  
Two Phase ◽  
Interfacial Pressure ◽  
Two Fluid Model ◽  
Two Fluid

Mathematical ill-posedness of the governing equations is one the main causes of numerical instability encountered in numerical simulation of two-phase flow using a two-fluid model. It is known that the ill-posedness can be mitigated if the difference between the average pressures of gas and liquid phases is taken into consideration appropriately. In the present work, it was investigated how the numerical stability of the one-dimensional, two-fluid model is influenced by the interfacial pressure terms that express the pressure difference between bubbles and continuous liquid phase in bubbly two-phase flow. Analyses were carried out for adiabatic air-water two-phase flow and subcooled flow boiling. It was confirmed that the interfacial pressure terms are effective to mitigate the numerical instability induced by the mathematical ill-posedness of the two-fluid model. However, the standard interfacial pressure terms deteriorated the numerical stability in some cases. It was found that the simplified model in which the spatial gradients of relative velocity and fluid density are eliminated is effective for the mitigation of numerical instability in wider analytical conditions.

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